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1. Field of the Invention
The system of the present invention relates to drilling and completing of high pressure/high temperature oil wells. More particularly, the present invention relates to a system and method FOR HYDRAULIC FRICTION CONTROLLED DRILLING AND COMPLETING GEOPRESSURED WELLS UTILIZING CONCENTRIC DRILL STRING OR STRINGS. The annular hydrostatic and increased frictional effects of multi-phase flow from concentric drill string or strings manages pressure and does not allow reservoir inflow or high annular flowing pressures at surface.
2. General Background of the Invention
In the general background of the applications and patents which are the precursors to this application, a thorough discussion of drilling and completing wells in an underbalanced state while the well was kept alive was undertaken, and will not be repeated, since it is incorporated by reference herein. The present inventor, Robert A. Gardes, the named patentee in U.S. Pat. Nos. 5,720,356 and 6,065,550 patented a method and system which covers among other things, the sub-surface frictional control of a drilling well by means of a combination of both annulus and standpipe or CTD fluid injection. His original patent covered methods and systems for drilling and completing underbalanced multi-lateral wells using a dual string technique in a live well. Through a subsequent improvement patent, he has also addressed well control through dual string fluid injection. Therefore, what is currently being accomplished in the art is the attempts to undertake underbalanced drilling and to trip out of the hole without creating formation damage thereby controlling the pressure, yet hold the pressure so that one can trip out of the well with the well not being killed and maintaining a live well.
The present inventor has determined that by pumping an additional volume of drilling fluid through a concentric casing string or strings, the bottom hole equivalent circulating pressure (ECD) can be maintained by replacing hydrostatic pressure with frictional pressure thus the wellbore will see a more steady state condition. The pump stops and starts associated with connections in the use of jointed pipe can be regulated into a more seamless circulating environment. By simply increasing the annular fluid rate during connections by a volume approximately equal to the normal standpipe rate, the downhole environment in the wellbore sees a near constant ECD, without the usual associated pressure spikes. For geopressured wells, the loss in hydrostatic pressure at total depth due to the loss of frictional circulating effects whenever the pumps are shut down (as in a connection) can cause reservoir fluids, especially high-pressured gas, to influx into the wellbore causing a reduction in hydrostatic pressure. In deep, high fluid density wells this xe2x80x9cconnection gasxe2x80x9d can become an operational problem and concern. This is especially true in certain critical wells that have a narrow operating envelope between equivalent circulating density (ECD) and fracture gradient.
Therefore, what has been developed by the present inventor is an innovative and new drilling technique to provide an additional level of well control beyond that provided with conventional hydrostatically controlled drilling technology. This process involves the implementation of one or more annular fluid injection options to compliment the standpipe injection through the jointed pipe drill string or through a coil pipe injection in a coiled tubing drilling (CTD) process. The method has been designed in conjunction with flow modeling to provide a higher standard of well control, and has been successfully field tested and proven.
The system and method of the present invention provides is a system for drilling geopressured wells utilizing hydraulic friction on the return annulus path downhole to impose a variable back pressure upon the formation at any desired level from low head, to balanced and even to underbalanced drilling. Control of the back pressure is dependent upon a secondary annulus fluid injection that results in additional frictional well control. Higher concentric casing annular injection rate leads to higher friction pressure, and lower fluid rates cause lower friction pressures and back pressures. For connections additional flow is injected into the annulus to offset the normal standpipe injection rate and maintain near constant bottom hole circulating rates and ECD on the formation.
Stated otherwise the invention provides a method of pressure controlling the drilling of wells, by providing a principal drill string; providing a plurality of concentric casing string or strings surrounding at least a portion of the principal drill string; and pumping a controlled volume of fluid down the plurality of concentric casing string or strings and returning the fluid up a common return annulus for both the principal drill string and microannulus strings, so that the friction caused by the fluid flow up the common return annulus is greater than the friction caused by the fluid flow of just the concentric casings or drill string to frictionally control the well.
Therefore, it is a principal object of the present invention to provide a drilling technique to give operators drilling critical high-pressure wells an additional level of well control over conventional hydrostatic methods utilizing hydraulic friction on the return annulus path downhole;
It is a further principal object of the present invention to provide multi phase annular friction created by hydraulic friction to control the well for kill operations, by having a secondary location for fluid injection in combination with the drill pipe or coiled tubing;
It is a further principal object of the present invention to utilize hydraulic friction on the return annulus path downhole to impose a variable back pressure upon the formation at any desired level from low head, to balanced and even to underbalanced drilling;
It is a further principal object of the present invention to provide a system of controlling well flow by matching injection and return annuli to achieve the desired high fluid injection rates at relatively low surface pressures and hydraulic horsepower, and the high return side frictional pressure losses that are needed for adequate flow control.